How can I subdivide this surface or what do I need to do to the surface to make it able to subdivide
Explanation

Probably that face used for the ground is an n-gon. It isn't possible to subdivide an n-gon directly to produce predictable results, all it does is add vertices to the perimeter.



On the left is a similar structure that has edges spanning to each opposite vertex. On the right the face was generated in one go by selecting all perimeter edges and pressing F to generate one face (an n-gon)



and that's OK until you try to apply a modifier like Subsurf, because you don't have any control over the way Blender internally constructs the n-gon geometry.



Solution

Judging by the geometry I see in your image, it might be possible to select the n-gon, then press Ctrl+F to get the faces menu and select option 'Triangulate Faces', this will make initial cuts. Then Ctrl+F again and select 'Tris to Quads`. This might produce the following geometry.



Realistically.

Once you get a bit more practice with Blender you'll probably approach making a tunnel in a different way.

An efficient way to make a tube/tunnel is to create a profile shape and then use that as a bevel object for a curve.